1. Field of the Invention
This invention relates to electrical measurement for testing using voltage probes with a panel circuit arrangement having electrical connectors in general, more particularly to microelectronic circuit board or chip node point and inspection point continuity testing fixtures.
2. Description of Prior Art
Structures for probing small pads in close proximity have been known and in use for some time, however, due to inherent problems of maintaining conformance of the probe to the site and area, limitations for ultra close spacing prior art has not, as yet, filled the need for the still advancing technology.
One such device utilizes spring loaded probes or so called by the industry, a "bed-of-nails" contact fixture. These fixtures consist of individual spring loaded probes that are pressed into holes drilled in insulating material, such as a flat sheet. The probes fixtures are used for contacting large area devices, such as printed circuit boards, and the like. This design, however, limits the spacing to no less than 0.050" (1.27 MM) center-to-center, due to the minimum diameter of the spring and the capabilities to wind a wire in coil configuration insertable into a probe.
Another such device is taught by Fowler in U.S. Pat. No. 3,906,363 wherein a wire is positioned between two plates with one end restrained and the other slideably engaged. The moveable end projects through the plate and contacts the element under test. The wire or needle deforms within its elastic limits, as a collapsing column when pressed onto the node points of the workpiece. The expense of drilling two corresponding p1ates is high and the needles have a tendency to run into each other when depressed limiting the reliability of this art.
U.S. Pat. No. 4,061,969 issued to Dean employs a series of pins embedded into a sealed flexible membrane with wires attached to the pins passing through an airtight seal. A vacuum is pulled within a chamber formed by the membrane causing the pins to obtain conformance with the workpiece under this negative pneumatic pressure. Dean also takes advantage of the previously described spring loaded probes in another embodiment.
Faure et al in U.S. Pat. No. 4,063,172 entitled, Multiple Site, Differential Displacement, Surface Contacting Assembly, applies a group of probes for multiple site chip clusters with a plurality of cams cooperating with followers to independently locate each cluster or groups of probes so as to compensate for accumulated tolerance or shrinkage in long substrates. Clusters of probes are moved with a single adjustment laterally as a group with the probes taking advantage of the collapsing column or buckling beam configuration for compliance.
Prior art also utilizes a fixed point probe card consisting of needle point probes mounted on printed circuit boards. These fixtures are widely used for probing integrated circuits and small geometry devices. This art is limited in its physical size as no more than 150 points per square inch (23 points per square centimeter) and about 200 probes total can be mounted on a single probe card. This limitation exists due to the fact that the probes are mounted pointing axially around a circle with a flat horizontal spring action providing the necessary conformance to the substrate pads.
For background purposes and as indicative of the art to which this invention relates, reference may be made to U.S. Pat. No. 4,285,563 issued to Crosier et al and also U.S. Pat. No. 4,298,239 of Montalto et al entitled, Test Access Apparatus.